1. Field of the Invention
The present invention relates to a recording medium, particularly to an ink-jet recording medium. The present invention also relates to an ink-jet recording method employing the recording medium.
2. Related Background Art
Various recording mediums are used for ink-jet recording, including coated-paper sheets, glossy-paper sheets, OHP-recording films (recording films for overhead projectors), etc. An example of the coated paper is the one disclosed in Japanese Patent Publication No. 3-26665 which comprises a base paper sheet and a coating layer composed of fine powdery silica and a water-soluble binder such as polyvinyl alcohol. An example of the glossy paper is the one disclosed in Japanese Patent Publication No. 3-25352 which comprises a cast-coated paper sheet and a surface layer composed of polyvinyl alcohol of a saponification degree of 50 to 90 mol % and a crosslinking agent. An example of the OHP-recording films is the one which is disclosed in Japanese Patent Application Laid-Open No. 60-220750 which comprises a polyester film and a hydrophilic surface layer composed or a water-soluble polyvinyl alcohol of a saponification degree of 70 to 90 mol %.
With improvements in performance of ink-jet recording apparatuses in recording speed, multiple color recording, and so forth, the recording medium therefor is required to be improved to have the properties below simultaneously:
(1) The recording medium has higher ink-absorbency (a larger ink absorption capacity, and quicker ink absorption). PA0 (2) The recorded dots have high optical density with definite circumference. PA0 (3) The recorded dots have a shape approximate to a true circle with smooth circumference. PA0 (4) The recording medium changes little its properties and does not curl with changes of temperature and humidity. PA0 (5) The recording medium does not cause blocking. PA0 (6) The recorded image is stable and does not deteriorate in long-term storage (particularly under a high temperature and a high humidity). PA0 (7) The recording medium itself is stable and does not deteriorate in long-term storage (particularly under a high temperature and a high humidity). PA0 (i) polyvinyl alcohol or a derivative thereof, PA0 (ii) polyalkylene oxide or derivative thereof, and PA0 (iii) a hydrophilic acrylic resin composed of a copolymer of a first vinyl monomer having a cationic group with a second vinyl monomer having a hydrophobic group.
OHP-recording sheets are additionally required to have excellent transparency.
These required conditions are inconsistent with each other, and prior art technique does not give a recording medium satisfying simultaneously the above required properties. For example, the above-mentioned recording mediums of the prior art, although they are acceptable in the recorded dot shape and anti-blocking properties, do not have sufficient ink absorbency, causing disadvantageously non-fixation of excessive ink, at regions where a larger amount of ink is deposited, to give rise to image disturbance and irregular image density, and in particular in color printing to give muddiness of color at the border of different colors.
With the progress of ink-jet recording in recording speed, recording density, and color printing, deterioration of image quality caused by insufficient ink fixation has become a serious problem.
The recording medium described in Japanese Patent Publication No. 3-29596, which has an ink-receiving layer mainly composed of polyvinylpyrrolidone has relatively high ink absorbency at a normal temperature and a normal humidity, but has disadvantages of low ink-drying speed and liability of blocking at a higher temperature and a higher humidity; and low resistance to scratching owing to low mechanical strength of the recording surface.
The recording mediums having an ink-receiving layer composed mainly of polyvinyl alcohol as mentioned above as the prior art, which are satisfactory in anti-blocking properties and the mechanical strength of the recording face, have disadvantages of deterioration of the recording medium to cause decrease of ink absorbency, and deterioration of an recorded image such as feathering of ink dots and lowering of sharpness of a recorded image during long-term storage at a higher temperature and a higher humidity.